Noninvasive Cortical Stimulation in Neurorehabilitation: A Review

In TMS, (A) a brief strong electric current traveling through the coil (B) results in a magnetic field that passes through (C, D) the skull to produce electric currents in the cortex. The magnetic coil is positioned in this example using a frameless stereotactic device on the scalp overlying the target cortical site on the subject’s own MRI. Reprinted with permission of Jarmo Ruohonen.

Schematic of premovement interhemispheric inhibition (IHI) in a healthy volunteer performing a reaction time task. Note the initial deep inhibition from the resting to the active hemisphere that reverses into facilitation close to movement onset. Abbreviation: EMG, muscle activity measured by electromyography.

(A) A hypothesis emerging from recent investigations is that normal motor control results from a proper balance of inhibitory and excitatory interactions between both hemispheres. (B) After subcortical stroke (represented by circle with cross hatching), this balance of inhibition is disrupted, such that the inhibition from the nonlesioned to the lesioned hemisphere is more prominent when the patient moves the paretic hand. Noninvasive cortical stimulation has been used in initial studies to enhance activity in the lesioned hemisphere or to downregulate activity in the nonlesioned hemisphere.